The invention is related to the field of optical devices, and in particular to optical devices employing surface patterning for enhanced light-matter interaction.
Deterministic Aperiodic Nano Structures (DANS) enable the realization of complex scattering resonances and nanoscale localized optical fields. DANS can be realized as inhomogeneous metal-dielectric structures in which the refractive index fluctuates over multiple length scales comparable to or smaller than the wavelength of light. These structures are designed by mathematical rules, which interpolate in a tunable fashion between periodicity and randomness. In particular, their reciprocal Fourier space (i.e., Fraunhofer diffraction pattern) ranges from a discrete set of δ-like Bragg peaks (i.e., pure point spectrum), such as for periodic and quasiperiodic crystals, to a continuous spectrum (i.e., absence of Bragg peaks) with short-range correlations, as encountered in amorphous systems. Due to a far richer structural complexity compared to periodic, quasiperiodic, and disordered random media, the Fourier space of DANS can encode non-crystallographic point symmetries with rotational axes of arbitrary order. The optical properties of surface plasmon-polaritons in quasi-crystal arrays of sub-wavelength nanoholes fabricated in metallic thin films have been the subject of recent research efforts, leading to demonstration of phenomena such as resonantly enhanced optical transmission, sub-wavelength imaging and super focusing effects.
Quasicrystal structures generally possess well-defined scattering peaks (i.e., pure point spectra) which can be arranged to display discrete rotational symmetries (i.e., rotations of finite order n=5, 8, 10, 12), known as non-crystallographic point symmetries, because they are incompatible with the translational invariance of regular periodic crystals. On the other extreme, disordered and amorphous structures may be characterized by diffused Fourier spectra. Structures having infinite-order rotational or circular symmetry in reciprocal space (i.e., Fourier space) have been constructed by a simple procedure that iteratively decomposes a triangle into five congruent copies. The resulting aperiodic tiling, named the Pinwheel tiling, has triangular elements (i.e., tiles) which appear in infinitely many orientations. Its diffraction pattern approximates continuous circular symmetry only in the limit of an infinite-size structure.